Neutron Capture Cross Section Measurements Research Articles

Neutron Capture Cross Section Measurement of Praseodymium in the Energy Region from 0.003 eV to 140 keV

The neutron capture cross section of praseodymium (141Pr) has been measured relative to the 10B(n,αγ) standard cross section in the energy region from 0.003 eV to 140 keV by the neutron time-of-flight (TOF) method with a 46-MeV electron linear accelerator (linac) of the Research Reactor Institute, Kyoto University (KURRI). An assembly of Bi4Ge3O12 (BGO) scintillators was used for the capture cross section measurement. In addition, the thermal neutron cross section (2,200 m/s value) of the 141Pr(n, γ)142Pr reaction has been also measured by an activation method at the heavy water thermal neutron facility of the Kyoto University Reactor (KUR). The thermal neutron flux was monitored with the 197Au(n, γ)198Au standard cross section. The above TOF measurement has been normalized to the current activation data (11.6±1.3 b) at 0.0253 eV. The evaluated data in JENDL-3.3, ENDF/B-VI, and JEF-2.2 have been in general agreement with the current result, except that the JENDL-3.3 and the JEF-2.2 values are clearly lower than the measurement in the cross section minimum region from about 10 to 500 eV.

Measurements of neutron capture cross-sections for ADS-related studies

Capture cross-sections on several isotopes relevant to accelerator driven systems for energy production and nuclear waste transmutation, and to stellar nucleosynthesis can be studied at the innovative neutron time of flight facility (n_TOF) at CERN. The experimental apparatus is based on a low-mass Si-based flux monitor and a set of C 6D 6 liquid scintillator detectors. The accurate reconstruction of the cross-sections relies on the pulse height weighting function technique. The set-up used in the measurements is here described. The first results on reference isotopes, Au, Ag and Fe, used to verify the accuracy of the method are presented.

Neutron capture cross section measurement of 20,22Ne for stellar nucleosynthesis

We have measured the neutron capture cross sections of 20Ne(n,γ) 21Ne and 22Ne(n,γ) 23Ne at stellar energy by detecting a discrete γ-ray feeding from a neutron capturing state to a low-lying state. In this work the non-resonant direct p-wave capture reaction process has been identified for the first time in the keV neutron capture reactions of Ne isotopes.

Neutron Capture Cross-Section Measurement of Rhodium in the Energy Region from 0.003 eV to 80 keV by Linac Time-of-Flight Method

The neutron capture cross section of rhodium has been measured in the energy region from 0.003 eV to 80 keV by the neutron time-of-flight method with a 46-MeV electron linear accelerator of the Kyoto University, Research Reactor Institute. An assembly of Bi4Ge3O12 (BGO) scintillators, which was composed of 12 pieces of BGO and placed at a distance 12.7 ± 0.02 m from the neutron source, was employed as a total energy absorption detector for the prompt capture gamma-ray measurement from the sample. In order to determine the neutron flux impinging on the capture sample, a plug of 10B powder sample and the 10B(n, αγ) standard cross section were used.The existing experimental data and evaluated capture cross sections in ENDF/B-VI, JENDL-3.2, and JEF-2.2 have been compared with the current measurement. Popov and Shapiro obtained poor energy resolution data in the resonance region with a lead slowing-down spectrometer. Furthermore, their data are a little higher than the current values above ˜1 keV. The experimental data measured by Weston et al., Hockenbury et al., Macklin and Halperin, Fricke et al., and Block et al. are somewhat higher than the current values. The data measured by Moxon and Rae are somewhat lower than the current values above ˜100 eV. The data measured by Wisshak et al. and Bokhovko et al. are in general agreement with the measurement above 4 keV within the experimental error. The evaluated data in ENDF/B-VI, JENDL-3.2, and JEF-2.2 have been in good agreement with the current result, although the JENDL-3.2 and the JEF-2.2 values are somewhat lower than the measurement in the cross section minimum region from 10 to 100 eV.The thermal neutron cross sections (2200 m/s values) measured by Seren et al. and Walker et al. are in good agreement with the current measurement (133.0 ± 0.93 b) within the experimental error. Other experimental data and the evaluated data are discrepant by 9 to 29% from the measurement.

Self-Shielding and Multiple Scattering Corrections for Neutron Capture Cross Section Measurements in Resonance Energy Range

Self-Shielding and Multiple Scattering Corrections for Neutron Capture Cross Section Measurements in Resonance Energy Range

Neutron Capture Cross Section Measurement of Praseodymium in the Energy Region from 0.003 eV to 140 keV

Neutron Capture Cross Section Measurement of Praseodymium in the Energy Region from 0.003 eV to 140 keV

Reinvestigation of 85Kr Branching in the Light of New 82, 84, 86Kr Neutron Capture Cross Section Measurements

High resolution neutron capture cross section measurements of 3 stable krypton isotopes, 82Kr, 84Kr and 86Kr, have been performed at the Geel Linear Accelerator (GELINA) on both resolved and unresolved resonance region. In addition, a total cross section measurement on 84Kr has also been performed in the energy range from 1 eV up to 120 kev. Accurate values of the Maxwellian–averaged capture cross section have been derived for all isotopes for stellar temperatures ranging from kT=5 up to 100 keV. A re–investigation of the s–process in the mass region around the prominent branching at 85Kr has been undertaken in the light of our new results.

Neutron Capture Cross Section Measurements of Tc-99 and Rh at Energies below 40 keV by Linac Time-of-Flight Method

The neutron capture cross sections of 99Tc and Rh have been measured relative to the 10B(n, α) standard cross section at energies below about 40 keV by the neutron time-of-flight (TOF) method using a 46 MeV electron linear accelerator (linac) at the Research Reactor Institute, Kyoto University (KURRI). A pair of C6D6 scintillation detectors has been used for the relative measurement of the 99Tc(n, γ) cross section, and the result has been normalized to the reference cross section value (19.57b) at 0.0253 eV in ENDF/B-VI. A total energy absorption detector, which was composed of 12 pieces of Bi4Ge3O12 (BGO) scintillators, was employed for the absolute capture cross section measurement of Rh. Both of the measured cross sections have been compared with the existing experimental data and the evaluated data in ENDF/B-VI, JENDL-3.2 and JEF-2.2.

Measurement of neutron capture cross-section of indium in the energy region from 0.003 eV to 30 keV

The neutron capture cross-section of indium (In) has been measured in the energy region from 0.003 eV to 30 keV by the neutron time-of-flight (TOF) method with a 46-MeV electron linear accelerator (linac) of the Research Reactor Institute, Kyoto University. An assembly of Bi 4Ge 3O 12 (BGO) scintillators, which was composed of 12 pieces of BGO and placed at a distance of 12.7±0.02 m from the neutron source, was employed as a total energy absorption detector for the prompt capture γ-ray measurement from the sample. In order to determine the neutron flux impinging on the capture sample, a plug of 10B powder sample and the 10B(n,α) standard cross-section were used. The data measured by Haddad et al. (Haddad, E., Friesenhahn, S., Lopez, W.M., 1963. Report of Gulf Energy and Environmental Systems, p. 3874) seem to be in good agreement with the present measurement. Popov et al. obtained the poor energy resolution data in the resonance region with a lead slowing-down spectrometer and the consistent data with the present above about 300 eV. The experimental data measured by Kononov et al. (Kononov, U.N., Jurlov, B.D., Poletaev, E.D., Timokhov, V.M., Manturov, G.N., 1977. Report of Obninsk, pp. 22–29) and Gibbons et al. (Gibbons, J.H., Macklin, R.L., Miller, P.D., Neiler, J.H., 1961. Phys. Rev. 122, 182) showed good agreement with the present values in the higher energy region. However, the data measured by Block et al. (Block R.C., Kaushal, N.N., Hockenbury, R.W., 1972. Conference on New Developments in Reactor Physics and Shielding at Kiamesha Lake, Vol. 2, p. 1107) seem to be a little higher than the present measurement above 800 eV. The evaluated data in ENDF/B-VI, JENDL-3.2, and JEF-2.2 have been in general agreement with the present result in the relevant energy region, although the JENDL-3.2 are higher than the measurement, the ENDF/B-VI and the JEF-2.2 from 2 to about 10 keV. Most of the previous experimental and the evaluated thermal neutron cross-sections are generally close to the present value of 199.6±5.6 b at 0.0253 eV.

Resonance neutron capture in 60Ni below 450 keV

High-resolution neutron capture cross-section measurements on 60Ni have been performed at the Geel Linear Accelerator in the energy range from 1 to 450 keV. An experimentally determined weighting function, obtained by a total energy detection set-up, has been applied to the measured capture spectra. The parameters of 275 resonances have been determined in a recent reanalysis using the FANAC R-matrix shape fitting code. Accurate values of the maxwellian-averaged capture cross section for stellar temperatures ranging from kT=5 to 100 keV, corresponding to different scenarios of s-process stellar nucleosynthesis, have been calculated. The distributions of partial radiative widths for s- and p-wave resonances have been derived. A correlation of 0.64 between capture and reduced neutron widths is compatible with the presence of nonstatistical effects in the capture of 60Ni.

129I targets for studies of nuclear waste transmutation

Nuclear incineration of long-lived fission products and minor actinides is being investigated as an alternative means of reactor waste disposal. 129I is of particular interest because of its long half-life and high mobility in the environment. Lead iodide targets of 129I for neutron capture cross-section measurements were prepared from 210 l fuel reprocessing waste solution containing 1.3 g l −1 iodine and other fission products. The iodine was separated by oxidation to I 2 and extraction into chloroform, reduction to iodide by sodium sulphite and re-extraction into an aqueous phase. Iodide was precipitated using lead nitrate and dried. The chemistry was carried out batch-wise using 400 ml starting solution each time and recycling the chloroform. An extraction efficiency of about 90%, determined by γ-ray spectrometry, was achieved.

Stellar neutron capture cross section of the rarest stable isotope 180mTa

The Back-n beam line of the China Spallation Neutron Source is the first white neutron facility in China. One of its goals is to perform radiative neutron capture cross-section (σnγ) measurements. To study the experimental backgrounds of this new facility, a measurement of the σnγ of 197Au was carried out with a C6D6 detector system at Back-n. Time-dependent backgrounds induced by the scattered neutrons and in-beam gamma-rays were measured and analyzed with natC and natPb samples. The black resonance filter technique was employed to evaluate the shape of the backgrounds and perform the normalization. Besides, Monte Carlo simulations of these backgrounds were carried out with the Geant4 toolkit. The simulated results were compared with the experimental ones and the good agreement found allowed us to validate the background evaluation method.

Neutron Capture and Total Cross-Section Measurements and Resonance Parameter Analysis of Zirconium up to 2.5 keV

Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute LINAC using metallic zirconium samples. The capture measurement was made at the 25-m flight station with a multiplicity-type capture detector, and the transmission total cross-section measurements were performed at the 25-m flight station with a 6Li glass scintillation detector. Resonance parameters were determined by a combined analysis of all 11 data sets (4 capture and 7 transmission) using the least-squares multilevel R-matrix code REFIT.The present measurements were undertaken to resolve discrepancies between common usage (ENDF/B-VI) and the recent measurements of Salah et al. for the 300-eV zirconium doublet. The present measurements support the Salah et al. conclusions. Specifically, the results confirm the assignment of J = 3 for the 91Zr 292.5-eV resonance and include all significant resonances up to 2.5 keV. The zirconium resonance parameters Γγ and Γn, determined in the present measurement, are compared with the ENDF/B-VI parameters.

Purity determination of super-enriched176Yb by neutron activation and thermal neutron capture cross section measurement of the high-spin (16+) isomer178m2Hf

Neutron activation analysis has been applied to determine the purity of super-enriched176Yb as well as a diagnostic to optimize yields from the P.A.R.I.S. mass separator at Orsay. In 25 mass separations carried out during 3 months, 910 mg of super-enriched176Yb2O3 were recovered from the original 7 g of176Yb2O3 (97.5% enrichment). Neutron activation analysis has shown that only two per thousand of the initially present174Yb remained in the super-enriched product. Using this176Yb super-enriched (99.998%) target, micro-quantities of the high spin (16+) isomer178m2Hf were produced by the (α,2n) reaction at the U-200 cyclotron in Dubna. Quantities of about 2·1012 atoms of this isomer have been irradiated by thermal neutron at the ORPHEE Reactor, Saclay. Only the neutron capture giving rise to the isomeric state 25/2− of179Hf has been measured, by detection γ-rays of this 25.1 days isomer. A cross section of 45±5 barns was obtained for178m2Hf(n,γ)179m2Hf.

Density of discrete levels in 116Sn.

Model fits were made to the cumulative distribution of all known levels (with spins [ital J][le]10) in [sup 116]Sn below an excitation energy of 4.1 MeV identified in a variety of experiments, and simultaneously to the density of [ital J]=0 and [ital J]=1 resonances inferred from neutron capture and total cross-section measurements in [sup 115]Sn+[ital n]. Neither the back-shifted Fermi-gas model nor the constant-temperature model provides a satisfactory fit over the entire energy range. The generalized superfluid model, with a level-density parameter and a spin-cutoff factor that are both energy dependent, does give a good fit, and the resulting best-fit parameter values are consistent with those found in other applications of this model.

14.5-MeV Neutron capture cross-section measurements in160Gd with activation technique

Activation cross-sections for neutron capture have been measured at an energy of 14.5 MeV for160Gd, relative to σ(160Gd(n, 2n)159Gd)=1975 mb. Gamma-ray spectra of the product nuclei were measured with a HP Ge-detector. By systematically varying the geometrical arrangement the corrections due to the influence of lower energy neutrons could be determined. The corrected activation capture cross-section at 14.5 MeV is found to be 1.0±0.2 mb.

The influence of water absorption in samples for neutron capture cross section measurements

Sample-related corrections for average neutron capture cross section measurements are complicated in the keV region due to the resonance structure. In particular, light mass nuclei present in chemical compounds of rare earth materials make corrections for neutron multiple-scattering and self-shielding difficult. Moreover, samples of chemical compounds such as oxides are hygroscopic. A Monte Carlo method has been developed by taking into account the effects caused by neutron slowing down into the resonance region due to the scattering from hydrogen and oxygen atoms. The validity of the calculated corrections has been investigated by comparing experimental data of oxide and metallic samples. The calculation method and related problems will be discussed.

Neutron capture cross section measurements of 155Gd and 157Gd from 1.1 to 235 keV

Neutron capture cross section measurements of 155Gd and 157Gd were made at the Japan Atomic Energy Research Institute linac in the energy range from 1.1 to 235 keV. The results were compared to other measurements and to the JENDL-2 evaluation. The analysis of the capture cross sections by the least squares method gives the following average resonance parameters: 10 4 S 0 = 3.00 ± 0.28, 10 4 S 1 = 3.7 ± 1.1, 〈 Γ s γ 〉 = 119 ± 29 eV, 〈 Γ p γ 〉 = 140 ± 60 eV for 155Gd; and 10 4 S 0 = 2.23 ± 0.57, 10 4 S 1 = 2.2 ± 0.7, 〈 Γ s γ 〉 = 115 ± 28 eV, 〈 Γ p γ 〉 = 129 ± 25 eV for 157Gd.

Neutron capture cross section measurement of 232Th in the energy range of 400–950 keV

Neutron capture cross sections of 232Th have been measured relative to 197Au in the neutron energy range of 425–950 keV. The monoenergetic neutrons were produced by a 7Li (p, n) reaction. The activation analysis technique was employed where γ-rays emitted by the product nucleus 233Th, were measured using a large volume high resolution Ge(Li) detector. A computer code “SAMPO” was used to extract the photopeak areas of characteristic γ-rays from the measured complex γ spectrum. The measured cross sections, after applying the various corrections are found to be in good agreement with the ones reported in the literature.

Macroscopic thermal neutron capture cross section measurements

The macroscopic thermal neutron-capture cross-section measurement in cased-well bores is discussed. The physical parameter measured is the formation capture cross section which is related to the type of fluid saturating the pore space. This measurement distinguishes between gas and water, gas and oil, and oil and water provided the water is saline. The physics of the measurement and the historical development of the instrumentation are reviewed. Important instrumentation elements are examined. The reasons for the limitation of the measurement to saline connate-water environments of modest to high porosity and simple lithology are listed and quantified. Current hardware and software developments that aim at more-sophisticated data acquisition and reduction are examined in detail. Other important applications such as production monitoring and enhanced-oil-recovery prospects are briefly discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>